Method of manufacturing chemical mechanical polishing layers

ABSTRACT

A method of making a polishing layer for polishing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate is provided, comprising: providing a liquid prepolymer material; providing a plurality of hollow microspheres; exposing the plurality of hollow microspheres to a carbon dioxide atmosphere for an exposure period to form a plurality of treated hollow microspheres; combining the liquid prepolymer material with the plurality of treated hollow microspheres to form a curable mixture; allowing the curable mixture to undergo a reaction to form a cured material, wherein the reaction is allowed to begin ≦24 hours after the formation of the plurality of treated hollow microspheres; and, deriving at least one polishing layer from the cured material; wherein the at least one polishing layer has a polishing surface adapted for polishing the substrate.

The present invention relates generally to the field of manufacture ofpolishing layers. In particular, the present invention is directed to amethod of manufacturing polishing layers for use in chemical mechanicalpolishing pads.

In the fabrication of integrated circuits and other electronic devices,multiple layers of conducting, semiconducting and dielectric materialsare deposited on or removed from a surface of a semiconductor wafer.Thin layers of conducting, semiconducting, and dielectric materials maybe deposited by a number of deposition techniques. Common depositiontechniques in modem processing include physical vapor deposition (PVD),also known as sputtering, chemical vapor deposition (CVD),plasma-enhanced chemical vapor deposition (PECVD), and electrochemicalplating (ECP).

As layers of materials are sequentially deposited and removed, theuppermost surface of the wafer becomes non-planar. Because subsequentsemiconductor processing (e.g., metallization) requires the wafer tohave a flat surface, the wafer needs to be planarized. Planarization isuseful in removing undesired surface topography and surface defects,such as rough surfaces, agglomerated materials, crystal lattice damage,scratches, and contaminated layers or materials.

Chemical mechanical planarization, or chemical mechanical polishing(CMP), is a common technique used to planarize substrates, such assemiconductor wafers. In conventional CMP, a wafer is mounted on acarrier assembly and positioned in contact with a polishing pad in a CMPapparatus. The carrier assembly provides a controllable pressure to thewafer, pressing it against the polishing pad. The pad is moved (e.g.,rotated) relative to the wafer by an external driving force.Simultaneously therewith, a chemical composition (“slurry”) or otherpolishing solution is provided between the wafer and the polishing pad.Thus, the wafer surface is polished and made planar by the chemical andmechanical action of the pad surface and slurry.

Reinhardt et al., U.S. Pat. No. 5,578,362, discloses an exemplarypolishing layers known in the art. The polishing layers of Reinhardtcomprise a polymeric matrix having hollow microspheres with athermoplastic shell dispersed throughout. Generally, the hollowmicrospheres are blended and mixed with a liquid polymeric material andtransferred to a mold for curing. Conventionally, strict processcontrols are required to facilitate production of consistent polishinglayers from batch to batch, day to day, and season to season.

Despite implementation of stringent process controls, conventionalprocessing techniques nevertheless result in undesirable variation(e.g., pore size and pore distribution) in polishing layers producedbatch to batch, day to day, and season to season. Accordingly, there isa continuing need for improved polishing layer manufacturing techniquesto improve product consistency, in particular pore.

The present invention provides a method of making a polishing layer forpolishing a substrate selected from at least one of a magneticsubstrate, an optical substrate and a semiconductor substrate,comprising: providing a liquid prepolymer material; providing aplurality of hollow microspheres; exposing the plurality of hollowmicrospheres to a carbon dioxide atmosphere for an exposure period of >3hours to form a plurality of treated hollow microspheres; combining theliquid prepolymer material with the plurality of treated hollowmicrospheres to form a curable mixture; allowing the curable mixture toundergo a reaction to form a cured material, wherein the reaction isallowed to begin ≦24 hours after the formation of the plurality oftreated hollow microspheres; and, deriving at least one polishing layerfrom the cured material; wherein the at least one polishing layer has apolishing surface adapted for polishing the substrate.

The present invention provides a method of making a polishing layer forpolishing a substrate selected from at least one of a magneticsubstrate, an optical substrate and a semiconductor substrate,comprising: providing a liquid prepolymer material; providing aplurality of hollow microspheres, wherein each hollow microsphere in theplurality of hollow microspheres has an acrylonitrile polymer shell;exposing the plurality of hollow microspheres to a carbon dioxideatmosphere for an exposure period of >3 hours to form a plurality oftreated hollow microspheres; combining the liquid prepolymer materialwith the plurality of treated hollow microspheres to form a curablemixture; allowing the curable mixture to undergo a reaction to form acured material, wherein the reaction is allowed to begin ≦24 hours afterthe formation of the plurality of treated hollow microspheres; and,deriving at least one polishing layer from the cured material; whereinthe at least one polishing layer has a polishing surface adapted forpolishing the substrate.

The present invention provides a method of making a polishing layer forpolishing a substrate selected from at least one of a magneticsubstrate, an optical substrate and a semiconductor substrate,comprising: providing a liquid prepolymer material, wherein the liquidprepolymer material reacts to form a poly(urethane); providing aplurality of hollow microspheres, wherein each hollow microsphere in theplurality of hollow microspheres has a poly(vinylidenedichloride)polyacrylonitrile copolymer shell and wherein thepoly(vinylidene dichloride)polyacrylonitrile copolymer shellencapsulates an isobutane; exposing the plurality of hollow microspheresto a carbon dioxide atmosphere by fluidizing the plurality of hollowmicrospheres using a gas for an exposure period of ≧5 hours to form aplurality of treated hollow microspheres, wherein the gas is >30 vol %CO₂; combining the liquid prepolymer material with the plurality oftreated hollow microspheres to form a curable mixture; allowing thecurable mixture to undergo a reaction to form a cured material, whereinthe reaction is allowed to begin ≦24 hours after the formation of theplurality of treated hollow rnicrospheres; and, deriving at least onepolishing layer from the cured material; wherein the at least onepolishing layer has a polishing surface adapted for polishing thesubstrate.

The present invention provides a method of making a polishing layer forpolishing a substrate selected from at least one of a magneticsubstrate, an optical substrate and a semiconductor substrate,comprising: providing a mold; providing a liquid prepolymer material;providing a plurality of hollow microspheres; exposing the plurality ofhollow microspheres to a carbon dioxide atmosphere for an exposureperiod of >3 hours to form a plurality of treated hollow microspheres;combining the liquid prepolymer material with the plurality of treatedhollow microspheres to form a curable mixture; transferring the curablemixture into the mold; allowing the curable mixture to undergo areaction to form a cured material, wherein the reaction is allowed tobegin ≦24 hours after the formation of the plurality of treated hollowmicrospheres; wherein the curable mixture undergoes the reaction to formthe cured material in the mold; and, deriving at least one polishinglayer from the cured material; wherein the at least one polishing layerhas a polishing surface adapted for polishing the substrate.

The present invention provides a method of making a polishing layer forpolishing a substrate selected from at least one of a magneticsubstrate, an optical substrate and a semiconductor substrate,comprising: providing a mold; providing a liquid prepolymer material,wherein the liquid prepolymer material reacts to form a poly(urethane);providing a plurality of hollow microspheres, wherein each hollowmicrosphere in the plurality of hollow microspheres has apoly(vinylidene dichloride)polyacrylonitrile copolymer shell and whereinthe poly(vinylidene dichloride)/polyacrylonitrile copolymer shellencapsulates an isobutane; exposing the plurality of hollow microspheresto a carbon dioxide atmosphere by fluidizing the plurality of hollowmicrospheres using a gas for an exposure period of ≧5 hours to form aplurality of treated hollow microspheres, wherein the gas is ≧98 vol %CO₂; combining the liquid prepolymer material with the plurality oftreated hollow rnicrospheres to form a curable mixture; transferring thecurable mixture into the mold; allowing the curable mixture to undergo areaction to form a cured material, wherein the reaction is allowed tobegin ≦24 hours after the formation of the plurality of treated hollowmicrospheres; wherein the curable mixture undergoes the reaction to formthe cured material in the mold; and, deriving at least one polishinglayer from the cured material by skiving the cured material to for theat least one polishing layer; wherein the at least one polishing layerhas a polishing surface adapted for polishing the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the C90 vs. temperature warm up curve for aplurality of hollow microspheres treated with nitrogen for an exposureperiod of eight hours.

FIG. 2 is a graph of the C90 vs. temperature warm up curve for aplurality of hollow microspheres treated with CO₂ for an exposure periodof three hours.

FIG. 3 is a graph of the C90 vs. temperature cool down curve for theplurality of hollow microspheres treated with nitrogen for an exposureperiod of eight hours.

FIG. 4 is a graph of the C90 vs. temperature cool down curve for theplurality of hollow microspheres treated with CO, for an exposure periodof three hours.

FIG. 5 is a graph of the C90 vs. temperature warm up curve for aplurality of hollow microspheres treated with CO₂ for an exposure periodof live hours.

DETAILED DESCRIPTION

Surprisingly, it has been found that the sensitivity of pore size inpolishing layers to process conditions can be significantly reducedthrough treatment of a plurality of hollow microspheres before they arecombined with a liquid prepolymer material to form a curable mixturefrom which the polishing layers are formed. Specifically, it has beenfound that by treating the plurality of hollow microspheres as describedherein, wider process temperature variations can be tolerated within abatch (e.g., within a mold), from batch to batch, from day to day, andfrom season to season, while continuing to produce polishing layershaving a consistent pore size, pore count and specific gravity. Theconsistency of pore size and pore count is particularly critical inpolishing layers incorporating the plurality of hollow microspheres,wherein the hollow microspheres in the plurality of hollow microsphereseach have a thermally expandable polymeric shell. That is, the specificgravity of the polishing layer produced using the same loading (i.e., wt% or count) of hollow microspheres included in the curable material willvary depending on the actual size (i.e., diameter) of the hollowmicrospheres upon curing of the curable material.

The term “poly(urethane)” as used herein and in the appended claimsencompasses (a) polyurethanes formed from the reaction of (i)isocyanates and (ii) polyols (including diols); and, (b) poly(urethane)formed from the reaction of (i) isocyanates with (ii) polyols (includingdiols) and (iii) water, amines or a combination of water and amines.

The term “gel point” as used herein and in the appended claims inreference to a curable mixture means the moment in the curing processwhen the curable mixture exhibits an infinite steady-shear viscosity anda zero equilibrium modulus.

The term “mold cure temperature” as used herein and in the appendedclaims refers to the temperature exhibited by the curable mixture duringthe reaction to form the cured material.

The term “maximum mold cure temperature” as used herein and in theappended claims refers to the maximum temperature exhibited by thecurable mixture during the reaction to form the cured material.

The term “gel time” as used herein and in the appended claims inreference to a curable mixture means the total cure time for thatmixture as determined using a standard test method according to ASTMD3795-00a (Reapproved 2006) (Standard Test Method for Thermal Flow,Cure, and Behavior Properties of Pourable, Thermosetting Materials byTorque Rheometer).

The liquid prepolymer material preferably reacts (i.e., cures) to form amaterial selected from poly(urethane), polysulfone, polyether sulfone,nylon, polyether, polyester, polystyrene, acrylic polymer, polyurea,polyamide, polyvinyl chloride, polyvinyl fluoride, polyethylene,polypropylene, polybutadiene, polyethylene imine, polyacrylonitrile,polyethylene oxide, polyolefin, poly(alkyl)acrylate,poly(alkyl)methacrylate, polyamide, polyether imide, polyketone, epoxy,silicone, polymer formed from ethylene propylene diene monomer, protein,polysaccharide, polyacetate and a combination of at least two of theforegoing. Preferably, the liquid prepolymer material reacts to form amaterial comprising a poly(urethane). More preferably, the liquidprepolymer material reacts to form a material comprising a polyurethane.Most preferably, the liquid prepolymer material reacts (cures) to form apolyurethane.

Preferably, the liquid prepolymer material comprises apolyisocyanate-containing material. More preferably, the liquidprepolymer material comprises the reaction product of a polyisocyanate(e.g., diisocyanate) and a hydroxyl-containing material.

Preferably, the polyisocyanate is selected from methylene his4,4′-cyclohexyl-isocyanate; cyclohexyl diisocyanate; isophoronediisocyanate; hexamethylene diisocyanate; propylene-1,2-dissocyanate;tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate;dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of hexamethylene diisocyanate;triisocyanate of 2,4,4trimethyl-1,6-hexane diisocyanate; urtdione ofhexamethylene diisocyanate; ethylene diisocyanate;2,2,4-trimethylhexamethylene diisocyanate; 2,4,4tri-methylhexamethylenediisocyanate; dicyclohexylmethane diisocyanate; and combinationsthereof. Most preferably, the polyisocyanate is aliphatic and has lessthan 14 percent unreacted isocyanate groups.

Preferably, the hydroxyl-containing material used with the presentinvention is a polyol. Exemplary polyols include, for example, polyetherpolyols, hydroxy-terminated polybutadiene (including partially and fullyhydrogenated derivatives), polyester polyols, polycaprolactone polyols,polycarbonate polyols, and mixtures thereof.

Preferred polyols include polyether polyols. Examples of polyetherpolyols include polytetramethylene ether glycol (“PTMEG”), polyethylenepropylene glycol, polyoxypropylene glycol, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds andsubstituted or unsubstituted aromatic and cyclic groups. Preferably, thepolyol of the present invention includes PTMEG. Suitable polyesterpolyols include, but are not limited to, polyethylene adipate glycol;polybutylene adipate glycol; polyethylene propylene adipate glycol;o-phthalate-1,6-hexanediol; poly(hexamethylene adipate) glycol; andmixtures thereof. The hydrocarbon chain can have saturated orunsaturated bonds, or substituted or unsubstituted aromatic and cyclicgroups. Suitable polycaprolactone polyols include, but are not limitedto, 1,6-hexanediol-initiated polycaprolactone; diethylene glycolinitiated polycaprolactone; trimethylol propane initiatedpolycaprolactone; neopentyl glycol initiated polycaprolactone;1,4-butanediol-initiated polycaprolactone; PTMEG-initiatedpolycaprolactone; and mixtures thereof. The hydrocarbon chain can havesaturated or unsaturated bonds, or substituted or unsubstituted aromaticand cyclic groups. Suitable polycarbonates include, but are not limitedto, polyphthalate carbonate and poly(hexamethylene carbonate) glycol.

Preferably, the plurality of hollow microspheres is selected from gasfilled hollow core polymeric materials and liquid filled hollow corepolymeric materials, wherein the hollow microspheres in the plurality ofhollow microspheres each have a thermally expandable polymeric shell.Preferably, the thermally expandable polymeric shell is comprised of amaterial selected from the group consisting of polyvinyl alcohols,pectin, polyvinyl pyrrolidone, hydroxyethylcellulose, methylcellulose,hydropropylmethylcellulose, carboxymethylcellulose,hydroxypropylcellulose, polyacrylic acids, polyacrylamides, polyethyleneglycols, polyhydroxyetheracrylites, starches, maleic acid copolymers,polyethylene oxide, polyurethanes, cyclodextrin and combinationsthereof. More preferably, the thermally expandable polymeric shellcomprises an acrylonitrile polymer (preferably, wherein theacrylonitrile polymer is an acrylonitrile copolymer; more preferably,wherein the acrylonitrile polymer is an acrylonitrile copolymer selectedfrom the group consisting of a poly(vinylidenedichloride)polyacrylonitrile copolymer and apolyacrylonitrile/alkylacrylonitrile copolymer; most preferably, whereinthe acrylonitrile polymer is a poly(vinylidenedichloride)polyacrylonitrile copolymer). Preferably, the hollowmicrospheres in the plurality of hollow microspheres are gas filledhollow core polymeric materials, wherein the thermally expandablepolymeric shell encapsulates a hydrocarbon gas. Preferably, thehydrocarbon gas is selected from the group consisting of at least one ofmethane, ethane, propane, isobutane, n-butane and isopentane, n-pentane,neo-pentane, cyclopentane, hexane, isohexane, neo-hexane, cyclohexane,heptane, isoheptane, octane and isooctane. More preferably, thehydrocarbon gas is selected from the group consisting of at least one ofmethane, ethane, propane, isobutane, n-butane, isopentane. Still morepreferably, the hydrocarbon gas is selected from the group consisting ofat least one of isobutane and isopentane. Most preferably, thehydrocarbon gas is isobutane. The hollow microspheres in the pluralityof hollow microspheres are most preferably gas filled hollow corepolymeric materials having a copolymer of acrylonitrile and vinylidenechloride shell encapsulating an isobutane (e.g., Expancel® microspheresavailable from Akzo Nobel).

The curable mixture comprises a liquid prepolymer material and aplurality of treated hollow microspheres. Preferably, the curablemixture comprises a liquid prepolymer material and a plurality oftreated hollow microspheres, wherein the plurality of treated hollowmicrospheres is uniformly dispersed in the liquid prepolymer material.Preferably, the curable mixture exhibits a maximum mold cure temperatureof 72 to 90° C. (more preferably, 75 to 85° C.).

The curable mixture optionally further comprises a curing agent.Preferred curing agents include diamines. Suitable polydiamines includeboth primary and secondary amines. Preferred polydiamines include, butare not limited to, diethyl toluene diamine (“DETDA”);3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof (e.g.,3,5-diethyltoluene-2,6-diamine);4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) (“MCDEA”);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenylmethane; p,p′-methylene dianiline (“MDA”); m-phenylenediamine (“MPDA”);methylene-bis 2-chloroaniline (“MBOCA”);4,4′-methylene-bis-(2-chloroaniline) (“MOCA”);4,4′-methylene-bis-(2,6-diethylaniline) (“MDEA”);4,4′-methylene-bis-(2,3-dichloroaniline) (“MDCA”);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane,2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the diamine curingagent is selected from 3,5-dimethylthio-2,4-toluenediamine and isomersthereof.

Curing agents can also include diols, triols, tetraols andhydroxy-terminated curatives. Suitable diols, triols, and tetraol groupsinclude ethylene glycol; diethylene glycol; polyethylene glycol;propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy) benzene;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(beta-hydroxyethyl)ether; hydroquinone-di-(beta-hydroxyethyl) ether; and mixtures thereof.Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy)benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol;and mixtures thereof. The hydroxy-terminated and diamine curatives caninclude one or more saturated, unsaturated, aromatic, and cyclic groups.

The plurality of hollow microspheres is exposed to a carbon dioxideatmosphere for an exposure period of >3 hours (preferably, ≧4.5 hours;more preferably, ≧4.75 hours; most preferably, ≧5 hours) to form aplurality of treated hollow microspheres.

Preferably, the carbon dioxide atmosphere to which the plurality ofhollow microspheres is exposed to form the plurality of treated hollowmicrospheres comprises ≧30 vol % CO₂ (preferably, ≧33 vol % CO₂; morepreferably, ≧90 vol % CO₂; most preferably, ≧98 vol % CO₂). Preferably,the carbon dioxide atmosphere is an inert atmosphere. Preferably, thecarbon dioxide atmosphere contains <1 vol % O₂ and <1 vol % H₂O. Morepreferably, the carbon dioxide atmosphere contains <0.1 vol % O₂ and<0.1 vol % H₂O.

Preferably, the plurality of hollow microspheres is exposed to thecarbon dioxide atmosphere by fluidizing the plurality of hollowmicrospheres using a gas to form the plurality of treated hollowmicrospheres. More preferably, the plurality of hollow microspheres isexposed to the carbon dioxide atmosphere by fluidizing the plurality ofhollow microspheres using a gas for the duration of an exposure periodof >3 hours (preferably, ≧4.5 hours; more preferably, ≧4.75 hours; mostpreferably, ≧5 hours) to form the plurality of treated hollowmicrospheres; wherein the gas comprises ≧30 vol % CO₂ (preferably, ≧33vol % CO₂; more preferably, ≧90 vol % CO₂; most preferably, ≧98 vol %CO₂) and wherein the gas contains <1vol % O₂ and <1 vol % H₂O. Mostpreferably, the plurality of hollow microspheres is exposed to thecarbon dioxide atmosphere by fluidizing the plurality of hollowmicrospheres using a gas for an exposure period of ≧5 hours to form theplurality of treated hollow microspheres; wherein the gas comprises ≧30vol % CO₂; and, wherein the gas contains <0.1 vol % CO₂ and <0.1 vol %H₂O.

The plurality of treated hollow microspheres are combined with theliquid prepolymer material to form the curable mixture. The curablemixture is then allowed to undergo a reaction to form a cured material.The reaction to form the cured material is allowed to begin ≦24 hours(preferably, ≦12 hours; more preferably ≦8 hours; most preferably ≦1hour) after the formation of the plurality of treated hollowmicrospheres.

Preferably, the curable material is transferred into a mold, wherein thecurable mixture undergoes the reaction to form the cured material in themold. Preferably, the mold can selected from the group consisting of anopen mold and a closed mold. Preferably, the curable mixture cantransferred into the mold by pouring or injecting. Preferably, the moldis provided with a temperature control system.

At least one polishing layer is derived from the cured material.Preferably, the cured material is a cake, wherein a plurality ofpolishing layers are derived from the cake. Preferably, the cake isskived, or similarly sectioned, into a plurality of polishing layers ofdesired thickness. More preferably, a plurality of polishing layers arederived from the cake, by skiving the cake into a plurality of polishinglayers using a skiver blade. Preferably, the cake is heated tofacilitate the skiving. More preferably, the cake is heated using aninfrared heating source during the skiving of the cake to form aplurality of polishing layers. The at least one polishing layer has apolishing surface adapted for polishing the substrate. Preferably, thepolishing surface is adapted for polishing the substrate through theincorporation of a macrotexture selected from at least one ofperforations and grooves. Preferably, the perforations can extend fromthe polishing surface part way or all of the way through the thicknessof the polishing layer. Preferably, the grooves are arranged on thepolishing surface such that upon rotation of the polishing layer duringpolishing, at least one groove sweeps over the surface of the substrate.Preferably, the grooves are selected from curved grooves, linear groovesand combinations thereof. The grooves exhibit a depth of ≧10 mils(preferably, 10 to 150 mils). Preferably, the grooves form a groovepattern that comprises at least two grooves having a combination of adepth selected from ≧10 mils, ≧15 mils and 15 to 150 mils; a widthselected from ≧10 mils and 10 to 100 mils; and a pitch selected from ≧30mils, ≧50 mils, 50 to 200 mils, 70 to 200 mils, and 90 to 200 mils.

Preferably, the method of making a polishing layer of the presentinvention, farther comprises: providing a mold; and, transferring thecurable mixture into the mold; wherein the curable mixture undergoes thereaction to form the cured material in the mold.

Preferably, the method of making a polishing layer of the presentinvention, further comprises: providing a mold; providing a temperaturecontrol system; transferring the curable mixture into the mold; whereinthe curable mixture undergoes the reaction to form the cured material inthe mold and wherein the temperature control system maintains atemperature of the curable mixture while the curable mixture undergoesthe reaction to form the cured material. More preferably, wherein thetemperature control system maintains a temperature of the curablemixture while the curable mixture undergoes the reaction to form thecured material such that a maximum mold cure temperature exhibited bythe curable mixture during the reaction to form the cured material is 72to 90° C.

An important step in substrate polishing operations is the determinationof an endpoint to the polishing. One popular in situ method for endpointdetection involves directing a light beam at the substrate surface andanalyzing the properties of the substrate surface (e.g., the thicknessof films thereon) based on the light reflected back from the substratesurface to determine the polishing endpoint. To facilitate such lightbased endpoint methods, the polishing layers made using the method ofthe present invention, optionally, further comprise an endpointdetection window. Preferably, the endpoint detection window is anintegral window incorporated into the polishing layer.

Preferably, the method of making a polishing layer of the presentinvention, further comprises: providing a mold; providing a windowblock; locating the window block in the mold; and, transferring thecurable mixture into the mold; wherein the curable mixture undergoes thereaction to form a the cured material in the mold The window block canbe located in the mold before or after transferring the curable mixtureinto the mold. Preferably, the window block is located in the moldbefore transferring the curable mixture into the mold.

Preferably, the method of making a polishing layer of the presentinvention, further comprises: providing a mold; providing a windowblock; providing a window block adhesive; securing the window block inthe mold; and, then transferring the curable mixture into the mold;wherein the curable mixture undergoes the reaction to form the curedmaterial in the mold. It is believed that securing of the window blockto the mold base alleviates the formation of window distortions (e.g.,window bulging outward from the polishing layer) when sectioning (e.g.,skiving) a cake into a plurality of polishing layers.

Some embodiments of the present invention will now be described indetail in the following Examples.

In the following Examples, a Mettler RC1 jacketed calorimeter outfittedwith a temperature controller, a 1 L jacketed glass reactor, anagitator, a gas inlet, a gas outlet, a Lasentec probe and a port on theside wall of the reactor for extending the end of the Lasentec probeinto the reactor. The Lasentec probe was used to observe the dynamicexpansion of the exemplified treated microspheres as a function oftemperature. In particular, with the agitator engaged the set pointtemperature for the calorimeter was ramped from 25° C. up to 72° C. andthen back down from 72° C. to 25° C. (as described in the Examples)while continuously measuring and recording the size of the exemplifiedtreated microspheres as a function of the temperature using the Lasentecprobe (with a focused beam reflectance measurement technique). Thediameter measurements reported in the Examples are the C90 chordlengths. The C90 chord length is defined as the chord length at which90% of the actual chord length measurements are smaller.

COMPARATIVE EXAMPLES C1-C2 AND EXAMPLE 1

In each of Comparative Examples C1-C2 and Example 1a plurality of hollowmicrospheres having a copolymer of acrylonitrile and vinylidene chlorideshell encapsulating isobutane (Expancel® DE microspheres available fromAkzoNobel) were placed in the bottom of the RC1 calorimeter reactor. Thereactor was closed up and a sweep stream of the gas noted in TABLE 1 wasthen continuously passed through the reactor for the noted exposureperiod to form a plurality of treated hollow microspheres. The sweepstream was then stopped. The agitator was then engaged to fluidize theplurality of treated hollow microspheres in the reactor. The set pointtemperature for the RC1 reactor jacket temperature controller was thenramped up linearly from 25° C. to 82° C. over one hour whilecontinuously measuring and recording the size of the treatedmicrospheres as a function of the temperature using the Lasentec probe(with a focused beam reflectance measurement technique). The set pointtemperature of the RC I reactor jacket temperature controller was thenmaintained at 82° C. for thirty (30) minutes before being rampedlinearly down from 82° C. to 25° C. over the next thirty (30) minuteswhile continuously measuring and recording the size of the treatedmicrospheres as a function of the temperature using the Lasentec probe(with a focused beam reflectance measurement technique). The set pointtemperature of the RC1 reactor jacket temperature controller was thenmaintained at 25° C. for the next thirty (30) minutes while continuouslymeasuring and recording the size of the treated microspheres as afunction of the temperature using the Lasentec probe (with a focusedbeam reflectance measurement technique).

TABLE 1 C90 vs. Temp. C90 vs. Temp. Exposure Period ramp up ramp downEx. Gas (in hrs) post exposure post exposure C1 nitrogen 8 FIG. 1 FIG. 3C2 CO₂ 3 FIG. 2 FIG. 4 1 CO₂ 5 FIG. 5 — 2 CO₂ 8 A — 3 (CO₂ + N₂) 

8 B —

 mixture of 33 vol % CO₂ and 67 vol % nitrogen A the C90 vs. temp. rampup exhibited by the plurality of treated microspheres from Example 2matched that exhibited by the plurality of treated microspheres fromExample 1. B the C90 vs. temp. ramp up exhibited by the plurality oftreated microspheres from Example 3 matched that exhibited by theplurality of treated microspheres from Example 2.

We claim:
 1. A method of making a polishing layer for polishing asubstrate selected from at least one of a magnetic substrate, an opticalsubstrate and a semiconductor substrate, comprising: providing a liquidprepolymer material; providing a plurality of hollow microspheres;exposing the plurality of hollow microspheres to a carbon dioxideatmosphere for an exposure period of >3 hours to form a plurality oftreated hollow microspheres; combining the liquid prepolymer materialwith the plurality of treated hollow microspheres to form a curablemixture; allowing the curable mixture to undergo a reaction to form acured material, wherein the reaction is allowed to begin ≦24 hours afterthe formation of the plurality of treated hollow microspheres; and,deriving at least one polishing layer from the cured material; whereinthe at least one polishing layer has a polishing surface adapted forpolishing the substrate.
 2. The method of claim 1, wherein the liquidprepolymer material reacts to form a material selected from the groupconsisting of poly(urethane), polysulfone, polyether sulfone, nylon,polyether, polyester, polystyrene, acrylic polymer, polyurea, polyamide,polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene,polybutadiene, polyethylene imine, polyacrylonitrile, polyethyleneoxide, polyolefin, poly(alkyl)acrylate, poly(alkyl)methacrylate,polyamide, polyether imide, polyketone, epoxy, silicone, polymer formedfrom ethylene propylene diene monomer, protein, polysaccharide,polyacetate and a combination of at least two of the foregoing.
 3. Themethod of claim 1, wherein the liquid prepolymer material reacts to forma material comprising a poly(urethane).
 4. The method of claim 1,wherein each hollow microsphere in the plurality of hollow microsphereshas an acrylonitrile polymer shell.
 5. The method of claim 1, whereinthe liquid prepolymer material reacts to form a poly(urethane); whereineach hollow microsphere in the plurality of hollow microspheres has apoly(vinylidene dichloride)polyacrylonitrile copolymer shell; whereinthe poly(vinylidene dichloride)/polyacrylonitrile copolymer shellencapsulates an isobutane; and wherein the plurality of hollowmicrospheres is exposed to the carbon dioxide atmosphere by fluidizingthe plurality of hollow microspheres using a gas for an exposure periodof ≧5 hours to form the plurality of treated hollow microspheres,wherein the gas is ≧30 vol % CO₂.
 6. The method of claim 1, furthercomprising: providing a mold; and, transferring the curable mixture intothe mold; wherein the curable mixture undergoes the reaction to form thecured material in the mold.
 7. The method of claim 6, furthercomprising: skiving the cured material to form the at least onepolishing layer.
 8. The method of claim 7, wherein the at least onepolishing layer is a plurality of polishing layers.
 9. The method ofclaim 8, wherein the liquid prepolymer material reacts to form apoly(urethane); wherein each hollow microsphere in the plurality ofhollow microspheres has a poly(vinylidene dichloride)polyacrylonitrilecopolymer shell; wherein the poly(vinylidenedichloride)polyacrylonitrile copolymer shell encapsulates an isobutane;and, wherein the plurality of hollow microspheres is exposed to thecarbon dioxide atmosphere by fluidizing the plurality of hollowmicrospheres using a gas for an exposure period of ≧5 hours to form theplurality of treated hollow microspheres, wherein the gas is ≧30 vol %CO₂.
 10. The method of claim 9, wherein the reaction is allowed to begin≦1 hour after the formation of the plurality of treated hollowmicrospheres.